Device for electronically controlling the propagation of radio frequency power



1956 B. KAZAN 2,772,377

DEVICE F OR ELECTRONICALLY CONTROLLING THE PROPAGATION OF RADIOFREQUENCY POWER Filed Aug. 29, 1951 R.F. INPUT I0 INVENTOR.

BENJAMIN KAZAN aired States DEVICE FOR ELECTRONICALLY CONTROLLING%EI;IVEI?RROPAGATION F RADIO FREQUENCY Benjamin Kazan, Princeton, N. J.,assignor to the United States of America as represented by the Secretaryof the Army The .invention described herein may be manufactured and usedby or for the Government for governmental purposes without the paymentto me of any royalty thereon.

This invention relates to an improved system for switching, attenuating,reflecting, modulating or phase shifting radio frequency power.

Heretofore, the electronic variation of radio frequency power in waveguide systems has been accomplished to a large degree by means of gasdischarge devices. The present invention is intended to accomplish thesame result, but instead of a gas filled space or chamber a high vacuummay be employed.

An object of this invention is to provide an improved system forvariably attenuating radio frequency energy in a wave guide.

A further object of the invent-ion is to provide an improved system forvariably absorbing, reflecting or switching electromagnetic wave energy.

Still another object of the invention is to provide an all electronicsystem for modulating energy propagated within a wave guide or similarstructure.

An additional object of the invention is to provide a variable phaseshifter. I

These objects are accomplished by providing an insulating (dielectric)or semi-conducting vane or window member in a conduit for propagatingelectromagnetic energy and by bombarding the said member with a beam ofhigh voltage (high velocity) electrons. It has been discovered that thelectrons impinging upon the insulating or semi-conducting member inducea state of conductivity in the member and thus provide a variablyconductive wave guide element. The conductivity of this element andconsequently, the energy propagated in the wave guide may be modulatedby modulating the electron beam.

Other and further objects of the invention will be found in thefollowing description of the invention taken in conjunction with theaccompanying drawing, in which Fig. l is a longitudinal section of afirst embodiment of the invention, and Fig. 2 is a transverse section ofa second embodiment of the invention.

Referring to Fig. 1, it represents a rectangular wave guide having theradio frequency energy introduced at 20. An insulating orsemi-conducting plate or window 11 is mounted transversely within saidwave guide. An electron gun structure generally indicated by the numeral12 is arranged to communicate with the interior of wave guide iiithrough an aperture 15 in a broad wall of the wave guide. The electrongun structure 12 may include the conventional cathode, grids,accelerating electrodes, and focusing electrodes, each of which isconnected to a .D.-C. potential divider 14 in a well known manner.Electron gun 12 is angulated with respect to the wave guide it) in orderthat the beam of electrons projected by the gun may illuminate thesurface of the window 11. The walls of the wave guide it) may serve asthe collector atent electrode for secondary electrons emitted from thewindow 11 and for primary electrons which are not absorbed by thewindow.

The junction of electron gun l2 and wave guide 10 should be designed tointroduce as little discontinuity in the wave guide structure as ispractical. Aperture 15 may comprise a narrow longitudinal slot centeredon a broad wall of the wave guide lid and cut parallel to the axis ofthe wave guide, or if more uniform illumination is desired, a largeraperture may be employed, and a plunger 13 may be provided to tune outthe discontinuity presented by the aperture. The plunger may be adjustedto reflect a very low impedance at the aperture.

The gun structure 12 may be designed by conventional techniques toprovide any type of electron beam desired. in addition, conventionaldeflecting electrodes may be provided to allow scanning of the surfaceof the window ii. A variable control element 16, which may comprise amechanical switch, a video amplifier, an oscillator, or other modulator,is inserted in the control grid circuit of the gun 12 to allow variationof the electron beam.

When the window 11 is bombarded with high voltage primary electrons, forexample, 10,000 volts, a state of induced conductivity will exist on thewindow which will be many times greater than the conductivity of theunbombarded material. In general, the induced conductivity arises on thesurface layer of the material, since the bombarding electrons do notpenetrate very far, for example, one micron at 10,000 volts.Electromagnetic wave energy which is propagated in the guide ill alongthe axis L will be reflected or attenuated to a degree dependent uponthe conductivity of the window 11. Control element 16 may be utilized tovary this conductivity in any desired manner.

Additional windows 17 and 18 are provided to ensure a high vacuum in thevicinity of the electron gun structure. It is evident that window 18 maybe omitted, if desired. However, it may be convenient to utilize windows17 and 18 to form a resonant cavity. in this case the windows 17 and 13may comprise metal diaphragms with dielectric centers. The spacing ofthe diaphragms may be adjusted to produce a standing wave having avoltage maximum at the window iii. In this manner variations inconductivity of the window ill will have a greater effect upon radiofrequency waves propagated within the wave guide iii. The diaphragms mayalso be utilized to counteract the discontinuity caused by aperture 15or to cancel energy reflected from window 11 back into the radiofrequency source.

It will be clear to anyone skilled in the art that various modificationsof the device in Fig. 1 may be constructed without departing from theprinciple of the invention. For example, the window iii may be bombardedby electron beams from opposite sides of the window. Instead ofemploying the walls of the wave guide llti as a collector for theelectrons, additional electrodes may be inserted within the wave guide,provided that they do not interfere with the propagation of the edit;frequency energy. Several of the units may be employed in cascade or intandem relationship, and thus, two units may provide successiveattenuation or reflection in a single wave guide, or alternateattenuation or refi ction in a pair of wave guides. The window it may belaminated and may consist of a first material, such as an insulator, andanother material, such as a semi-conductor which is coated on theinsulator in a thin layer. Among the well known insulators orsemi-conductors which may be employed are mica, glass, aluminum oxide,arsenic oxide, antimony sulphide, selenium, silica, and magnesiumfluoride.

The wave conduit and the electron gun may have any configuration andneed not be rectangular or round. In fact, the invention is notrestricted to wave guides but may be employed to vary the transmissioncharacteristics of a coaxial line or the resonant characteristics of acavity resonator. Furthermore, the variable conductivity element may beemployed in a stub or spur line which is coupled to the maintransmission line. For example, a closed ended stub wave guide one-halfof a guid Wave length long may be attached .as a branch guideperpendicular to a broad wall of a main rectangular wave guide. Thevariable conductivity window may be placed a quarter wave length fromthe closed end of the stub, so that causing the window to becomeconductive will vary the short circuit normally reflected at thejunction of the main and stub wave guides. It should be noted that theconstruction in Fig. 1 is merely illus trative of the principle of theinvention, which should not be unduly limited to this embodiment.

Another embodiment of the invention is shown in Fig.2. Elementscorresponding with those in Fig. 1 are designated by correspondingprimed reference numerals; however, Fig. 2 illustrates a transversesection, while Fig. 1 illustrates a longitudinal section. The window 11has been replaced by a longitudinal vane element 11, which may becentered or located off center of the wave guide 10'. The vane 11 mayassume any desired configuration, and any of the conventional matchingmeans such as end-notching or tapering may be employed. Electron gun 12'may conveniently communicate with the wave guide 10 through a centrallongitudinal aperture 315, in the embodiment shown. As in Fig. 1,matching means and vacuum sealing devices may be employed. Variousmodifications are obvious, as indicated previously.

Radio frequency energy propagated in wave guide 10' with the electricvector substantially parallel to the major surface of the vane 11' willbe attenuated to a degree dependent upon the conductivity induced by theelectron bombardment.

Although it has not been set forth above, it is evident to anyon skilledin the art that the invention illustrated in Figs. 1 and 2 will serve asa variable phase shifter without modification.

What I claim as my invention is:

1. A radio frequency component comprising a hollow pipe wave guidesection, a dielectric element in said section, means for introducingelectromagnetic waves into said section with the electric field parallelto a substan- 4. tial dimension of said dielectric element, and meansbombarding said dielectric element with a beam of high voltage lectronsfor varying the conductivity of said dielectric element to variablyattenuate said electromagnetic waves.

2. The component described in claim 1 wherein said wave guide section isevacuated, said dielectric element is a transverse window in saidsection, said electromagnetic waves are propagated through said window,and said means producing a beam of high voltage electrons includes meansfor modulating said beam.

3. A variabl attenuator comprising a hollow pipe wave guide section,means for projecting a beam of high voltage electrons into said Waveguide section, a plate element in said wave guide section and in thepath of said electrons, said plate element having a conductivity whichvaries in respons to bombardment to said electrons, means forintroducing electromagnetic energy into said wave guide section with theelectric field parallel to a substantial dimension of said plateelement, means for maintaining a high vacuum in said wave guide sectionin the vicinity of said plate element, and means for varying the numberof electrons in said beam.

4. The attenuator described in claim 3 wherein said plate element is atransverse dielectric window in said wave guide section, said means forprojecting a beam of high voltage electrons comprises an electron gunpositioned at an acute angle with respect to said section and coupled tosaid section through an aperture in the wall thereto, and said componentfurther includes means for effectively eliminating the discontinuity ofsaid aperture.

5. The component described in claim 3 wherein said plate element is alongitudinal dielectric member in said section.

References Cited in the file of this patent UNITED STATES PATENTS2,241,976 Blewett et al May 13, 1941 2,317,140 Gibson Apr. 20, 19432,338,237 Fremlin Jan. 4, 1944 2,413,385 Schmidt Dec. 31, 1946 2,527,632Graham Oct. 31, 1950 2,543,039 McKay Feb. 27, 1951 2,557,961 Goldsteinet al. June 26, 1951 2,589,704 Kirkpatrick et al Mar. 18, 1952 2,611,101Wallauschek Sept. 16, 1952 2,643,297 Goldstein et al. June 23, 1953

